Elastomeric sealant composition

ABSTRACT

A carbon reinforced, partially cross-linked butyl rubber matrix sealant composition as described is particularly suitable for use as a self-healing tire puncture sealant. The sealant composition comprises a high average molecular weight butyl rubber and a low average molecular weight butyl rubber in a ratio of high to low molecular weight butyl rubber of between about 20/80 to 60/40, in admixture with a tackifier present in an amount between about 55 and 70 weight % of the composition. A partially hydrogenated block copolymer may be included in the admixture.

FIELD OF THE INVENTION

The sealant composition of this invention was developed as aself-healing tire puncture sealant. As a tire sealant, it is adapted forapplication to the internal surface of a rubber tire and is intended toseal puncture holes in the tread region under widely varying temperatureconditions. Being suitable as a tire sealant, the sealant composition ofthis invention is applicable to other, similar as well as less severe,uses.

BACKGROUND OF THE INVENTION

A suitable self-healing tire puncture sealant must withstand wintertimetemperatures to which tires are subjected when standing idle. Such asealant must also withstand the high temperatures to which tires areheated under summertime driving conditions. These temperatures typicallyrange from -20° F to 270° F. A suitable tire sealant must be capable ofsealing punctures when the puncturing object is retained in the treadand also when the puncturing object is removed. Thus, a tire sealantmust be capable of adhering to the puncturing object as it works againsta flexing tire during travel and must be capable of adhering to itselfto seal the puncture after removal of the puncturing object. Inaddition, the sealant must remain effective for an extended period oftime. These conditions require a combination of flexibility, tackinessand strength that are among the most demanding required of any sealantcomposition. Finally, a suitable tire sealant must be susceptible toeconomical formulation and application.

Because butyl rubber exhibits low air permeability and high resistanceto aging, the prior art has attempted to utilize butyl rubber as a basiccompound of sealants. Exemplary of such prior art are U.S. Pat. Nos.2,756,801; 2,765,018, and 2,782,829. The sealant compositions describedin such prior art, however, are inadequate at the temperature extremesto which automatic tires are subjected considering the requirements thatsuch sealant compositions must be resistant to creep and must be selfhealing.

SUMMARY OF THE INVENTION

The sealant composition of this invention is formulated with a carbonreinforced curable butyl rubber matrix and certain modifiers to achievethe necessary mechanical strength, thermal stability, and sealingcapabilities required to a commercially acceptable self-healing tirepuncture sealant. The sealant composition comprises a combination ofpartially cross-linked (i.e. partially cured) high and low molecularweight butyl rubbers, a tackifier, and a carbon reinforcer. The weightratio of high molecular weight to low molecular weight butyl rubber mayvary from 20/80 to 60/40. The tackifier constitutes about 55-70 wt. % ofthe composition and the carbon reinforcer constitutes up to about 17 wt.% of the composition, the balance being the cross-linked rubberconstituents. To aid in maintaining sufficient tackiness and thermalstability at elevated temperatures, a thermoplastic and elastomericpartially-hydrogenated block copolymer may be included up to about 10wt. % of the composition, the block copolymer having a generalconfiguration of A-(B-A)₁₋₅ wherein prior to hydrogenation each A is amonovinyl arene polymer block and each B is a conjugated diene polymerblock.

The sealant composition may be applied by a variety of means. Forpurposes of tire sealing, the sealant composition may be formulated as asprayable composition that cures in situ or as a composition that isfirst cured in sheet form and then applied. For other purposes, thesealant composition may be extruded or brushed onto a substrate. Asuitable solvent, such as toluene, may be employed in the preparation ofthe sealant composition. The weight percentages specified herein,however, are on a solvent-free basis, unless otherwise noted.

DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of a cross-section of a vehicle tireillustrating one embodiment of the invention in which the sealantcomposition layer is located on the innermost surface of the tire behindthe tread;

FIG. 2 is a perspective view similar to FIG. 1, illustrating a secondembodiment of the invention in which the subject sealant layer islocated behind the tread portion of the vehicle tire and between an airimpervious film conventionally employed in a tubeless tire and thecarcass portion of the tire;

FIG. 3 is a graph showing Modulus of Elasticity vs. Strain for a sealantcomposition having a high to low molecular weight butyl rubber ratio ofabout 60/40 and a sealant composition having a high to low molecularweight butyl rubber ratio of about 35/65 to 45/55; and FIG. 4 is across-sectional view of a bicycle tire illustrating another embodimentof the invention in which the sealant composition layer is locatedbehind the tread portion of the tire between the innermost surface ofthe carcass portion of the tire and the tire's inner tube.

DETAILED DESCRIPTION OF THE INVENION

The copolymer matrix which provides the strength and continuity of thesealant composition of this invention is herein termed "butyl rubber".Butyl rubber is intended to include copolymers of 96-99 wt.% isobutyleneand 4-1 wt.% isoprene (Butyl IIR) as well as other rubbery copolymers ofa major proportion (i.e., over 50% by weight) of an issolefin havingfrom 4 to 7 carbon atoms with a minor proportion by weight of an openchain conjugated diolefin having from 4 to 8 carbon atoms. The copolymermay consist of from 70 to 99.5% by weight of an isomonoolefin such asisobutylene or ethyl methyl ethylene copolymerized with from 0.5 to 30%by weight of an open chain conjugated diolefin such as isoprene;butadiene -1,3; piperylene; 2,3- dimethyl-butadiene -1,3; 1,2-dimethyl-butadiene -1,3 (3-methyl pentadiene -1,3); 1,3 -dimethylbutadiene -1,3; 1-ethyl butadiene -1,3 (hexadiene -1,3); 1,4-dimethylbutadiene -1,3 (hexadiene -2,4); the copolymerization being effected bythe usual manner of copolymerizing such monomeric materials.

A high molecular weight butyl rubber, as this term is used herein,refers to butyl rubber having an average molecular weight in excess of100,000. While the use of butyl rubber having an average molecularweight in excess of 300,000-400,000 will not detract from the sealingqualities of the sealant, such butyl rubber is comparatively difficultto dissolve and combine with other constituents, as well as difficult toapply via an air spraying tehcnique. Thus the preferred weight range forthe high molecular weight butyl rubber is from 100,000 to about300,000-400,000. Low molecular weight butyl rubber, as the term is usedherein, refers to butyl rubber having an average molecular weight, andtherefore viscosity, substantially less than, on the order of about1/10th, that of the high molecular weight butyl rubber. Because of thepresent commerical availability, the preferred molecular weight rangefor low molecular weight butyl rubber is from 10,000 to 30,000.

Cross-linking of the butyl rubber constituents may be effected by one ofthe known sulfur or quinoid systems. Although butyl rubber may be curedusing a vulcanization process (sulfur and accelerators such asmercaptobenzothiazole), such a cure results in a rubber that over timeis subject to degredation caused by oxygen or ultraviolet radiation.Such degredation may be partly prevented through the use ofantioxidants, such as diphenyl - p - phenylene- diamine,phenyl-beta-naphthylamine and hydroquinone, and antiozonants, such asN,N'-di (2-octyl) -p- phenylenediamine and N-(1-3-demethyl-butyl) -N'-phenyl-p-phenylenediamine. Nevertheless, the characterists of theresulting sealant change sufficiently over time to make a quinoid curingsystem preferable to vulcanization for the tire sealing applications,where the sealant must be capable of lasting years in a harshenvironment. Quinoid cures depend of cross-linking through the nitrosogroups of aromatic nitroso compounds. In the quinoid curing system,p-quinone dioxime ("G-M-F") and p,p-di-benzoylquinone dioxime arepreferred as the curing agents. Other suitable curing agents includedibenzoyl-p-quinone dioxime ("Dibenzo G-M-F"), p-dinitrosobenzene andN-Methyl-N, 4-dinitrosoanilene, the latter two being available on a claybase as "Polyac" from E. I. duPont Nemours & Co. and as "Elastopar" fromMonsanto Chemical Co., respectively. The cross-linking activators whichmay be employed in the sealant composition include inorganic peroxides,organic peroxides (including diaroyl peroxides, diacyl peroxides andperoxyesters) and polysulfides. Exemplary are lead peroxide, zincperoxide, barium peroxide, copper peroxide, potassium peroxide, silverperoxide, sodium peroxide, calcium peroxide; metallic peroxyborates,peroxychromates, peroxycolumbates, peroxydicarbonates,peroxydiphosphates, peroxydisulfates, peroxygermanates,peroxymolybdates, peroxynitrates, magnesium peroxide, sodiumpryophosphate peroxide, and the like; the organic peroxides such aslauryl peroxide, benzoyl peroxide, 2,4-dichlorobenzoyl peroxide, t-butylperoxybenzoate, dibenzoyl peroxide, bis (p-monomethoxy-benzoyl)peroxide, p-monomethoxy-benzoyl peroxide, bis (p-nitrobenzoyl) peroxide,and phenacetyl peroxide; the metallic polysulfides such as calciumpolysulfide, sodium polysulfide, potassium polysulfide, bariumpolysulfide, and the like and the organic polysulfides such as the alkylpolysulfides, aryl polysulfides, aralkyl polysulfides, which possess thegeneral formula R-(S)_(x) -R where R is a hydrocarbon group and x is anumber from 2 to 4. The actual cross-linking agent is believed to be theoxidation product of quinone dioxime, p-dinitroso benzene.

The curing agent/cross-linking activator combination which has beenfound to result in the shortest gel time is the p-quinonedioxime/benzoyl peroxide combination. The preferred concentration ofp-quinone dioxime is 2-4% by weight of butyl rubber. The preferredconcentration of benzoyl peroxide is 7-10% by weight of butyl rubber.

Accelerators may be employed as appropriate. For example, cobaltnapthenate may be used in combination with t-butyl peroxybenzoate, andchloranil (2,3,5,6 - tetrachloro - 1,4 - benzoquinone) may be used incombination with t-butyl peroxybenzoate or benzoyl peroxide.

The tackifying agent serves two functions. First it decreases theelastic modulus of the sealant composition and thus increases itsability to self-heal over a puncture wound. Second, it increases thesealant composition's tack, i.e., its ability to adhere to otherobjects. The several classes of tackifiers which are suitable for use inthe sealant composition of this invention include low temperaturetackifiers, which associate primarily with the elastomeric compounds,and high temperature tackifiers, which associate primarily with the morerigid components such as the end blocks of the block copolymers.Examples of classes of low temperature tackifiers are syntheticpolyterpenes, thermoplastic olefins, pentaerythritol esters ofhydrogenated rosins, and termoplastic hydrocarbons. High temperatureclasses of tacifiers include triethylene glycol esters of hydrogenatedrosins, vinyl toluene copolymers, alkyl aromatics and coumarone-indenes.Methyl esters of hydrogeanated rosins, also suitable, are thought toassociate with both phases. Preferred tackifiers are fluid monoolefinpolymers of moderate viscosity, such as those consisting of essentiallybutylene (1-butene, 2-butene and isobutylene) with the balance beingisoparaffins, having average molecular weights in the range of 500 to5,000, terpene polymer resins such as polymerization products ofB-pinene, and low molecular weight styrene polymer resins such aspolymerization products of A-methylstyrene.

The reinforcing agent provides tensile strength to the sealant. It maybe of any one or more of a large number of well known substancesprovided that one of these substances must be finely divided carbon.Carbon, such as carbon black, provides reaction sites for the curingprocess, and preferably comprises at least 1% of the solids by weight.The substance comprising the remainder of the reinforcing agent mayeither be carbon black or some other suitable substance selected on thebasis of the desired color of the sealant. The reinforcing agent shouldbe present in an amount not exceeding 17% of the solids by weight. Abovethis concentration, the sealant composition has an unsuitably hightensile strength. Examples of well known reinforcing agents for butylrubbers include zinc oxide, aluminum hydrate, lithopone, whiting, clays,hydrated silicas, calcium silicates, silicoaluminates, magnesium oxide,and magnesium carbonate.

The block copolymer constituent, prior to hydrogenation, is composed of"A" blocks of monovinyl arene polymers including styrene, alpha methylstyrene, ring alkylated styrenes, and the like, as well as mixturesthereof, and "B" blocks of conjugated diene polymers having 4 to 10carbon atoms per monomer molecule, including butadiene and isoprene. TheA blocks make up the end groups and typically comprise about one thirdof the copolymer by weight, and the B blocks make up the mid groups andthe balance of the copolymer. The copolymer is partially hydrogenated sothat the conjugated diene block segments are substantially fullysaturated. The monovinyl arene polymer block segments are notappreciably saturated. Hydrogenation in this fashion enhances theutility of the block copolymer as an oxidation and hightemperature-degradation resistant constituent of the sealantcomposition. The average molecular weight of the copolymer is in therange of about 60,000 to 400,000. Block copolymers of this type aredescribed in U.S. Pat. No. 3,595,942.

The sealant composition constituents are either soluble or dispersablein hydrocarbon and chlorinated solvents, exemplary of which are toluene,hexane, heptane, naptha, trichloroethylene and cyclohexane.Tetrahydrofuran is also a suitable solvent. Combination of the abovesolvents can also be used. Toluene has been found to be the mostsuitable.

Within the ratio of high molecular weight to low molecular weight butylrubber defined herein, 20/80 to 60/40, the resultant sealant compositionis capable of maintaining its adherence to a tire substrate while beingstretched by a tread-penetrating object, such as a nail; is capable ofadhering to the puncturing object, so as to form a seal about theobject; and is capable of healing itself so as to re-seal a puncturewound after the puncturing object is removed. High-low molecular weightbutyl rubber ratios outside of the herein-defined ratios do not providesealant compositions capable of meeting these parameters over therequired temperature ranges or capable of remaining elastic forsufficient periods of time and, hence, are unsatisfactory. Within theherein defined ratios of high-low molecular weight butyl rubbers, theresultant sealant composition modulus of elasticity is quite different.

Furthermore, a sealant composition having a ratio of high molecularweight to low molecular weight butyl rubber between about 35/65 to 45/55has unexpectedly superior properties. Its initial modulus of elasticity,that is to say its modulus of elasticity during initial elongation, isquite low. This property enhances the puncture sealing capabilities ofthe sealant composition in that a puncturing object will disrupt thesealant composition to a lesser extent. Consequently, the sealantcomposition in the vicinity of a puncture responds more quickly to abreak or tear in its continuity and the extent of puncturing damage isless.

While the ultimate tensile strength (i.e., the point of breakage duringthe elongation testing) and modulus of elasticity for sealantcompositions having high to low molecular weight butyl rubber ratioscomponents in the range of about 20/80 to 60/40 are generally the same,the manner in which the cured sealant compositions react duringelongation and prior to reaching ultimate tensile stength is quitedifferent within the range of about 35/65 to 45/55. Specifically and asmore graphically described in FIG. 3, it has been discovered that whilesealant compositions with a high to low molecular weight butyl rubberratio of about 60/40, line A of FIG. 3, were relatively strong duringlow strain situations, i.e., a relatively high modulus of elasticityduring initial elongation, a sealant composition with a high to lowmolecular weight butyl rubber ratio between about 35/65 to 45/55, line Bof FIG. 3, is relatively weak in such situations and has a relativelylow modulus of elasticity during its initial phases of elongation. Also,the latter's (line B) modulus of elasticity has an over-all increaseduring complete elongation of the cured composition to the point ofultimate tensile strength, while the former's (line A) modulus ofelasticity has an over-all decrease during the complete elongation tothe point of ultimate tensile strength. The importance of theseparticular factors is that the puncture sealing capability of a sealanthas been found to be much more important during initial elongation andlow strain situations rather than at the point of ultimate tensilestress or breakage. If the sealant is quite strong during the initialelongation, and when an object punctures the tire and the sealant layer,the remainder of the sealant has a tendency to pull away from thepuncture wound and therefore not seal the puncture. However, with thelatter, which has a low strength during the initial elongation, thesealant stays in position when it is punctured and therefore seals thewound much easier. Thus, since the sealant must elongate during the lowstrain situations in order to adequately seal a puncture, sealantcompositions having a high tensile strength during low strainsituations, as in the former, may not seal the puncture as consistently.On the other hand, during high strain situations such as presented by a40 to 50 psig internal tire pressure, it is not desirable to have thesealant flow if the tire is to remain inflated after a puncture has beensealed. This is accomplished by the present invention since afterinitial sealant elongation, the modulus of elasticity and the tensilestrength of the present composition increase continuously to the pointof ultimate tensile strength.

Because the sealant composition described herein has the unique abilityto resist oxidation, and to remain stable and effective over a widetemperature range, it has numerous applications, such as a caulkingcompound and as a roofing sealant, in addition to its utility as a tiresealant. Because the environment, to which a tire sealant is subjectedis the most severe, the following examples relate the sealantcomposition to this environment for purposes of illustration. It will beunderstood that the ratio of the essential ingredients may be variedwithin the ranges set forth above and that other compounding materialsmay be replaced by and/or supplemented with such other materials as maybe appropriate to deal with the environment contemplated.

With particular respect to the vehicle tire sealant embodiment and withreference to FIG. 1, a vehicle tire 10 conventionally includes a treadportion 12, a carcass portion 14 and side walls 16. In tubeless vehicletires it is generally desirable to employ a barrier layer or lining 18which is impermeable to air. The air impermeable lining 18 typicallyextends over the entire inner surface of the tire 10 from one beadportion 20 to the other bead portion 22. In accordance with theembodiment of the present invention illustrated in FIG. 1, a sealantlayer 24 is placed on the inside of the tire 10 against the air barrierlayer 18. The sealant layer 24 is arranged to lie principally behind thetread 12 of the tire 10 so that the sealant layer will principally serveto seal punctures occurring in the tread portion of the tire.

FIG. 2 illustrates another embodiment of the present invention wherein avehicle tire 10 has parts similar to those illustrated in FIG. 1, andidentified by like numerals. However, in this particular embodiment thesealant layer 24 is located between the carcass portion 14 of the tire10 and the air impermeable barrier layer 18. The vehicle tire embodimentillustrated in FIG. 1 normally occurs when the sealant layer 24 isapplied after the tire 10 has been formed and cured. The vehicle tireembodiment illustrated in FIG. 2 occurs when the sealant layer 24 isincorporated into tire 10 when the tire 10 is itself being formed andcured. The sealant layer may be formed and cured at the same time thevehicle tire is being manufactured to realize production economies,since the subject sealant layer can be cured at the temperatures, about350° F., employed in curing the other rubber components of the tire.When this is done, it is possible to located the sealant layer in eitherposition as depicted by FIGS. 1 and 2, whereas if the sealant layer isapplied after the tire is manufactured, it is only possible to placesuch a layer inside the air impermeable barrier as illustrated inFIG. 1. Finally, it should be noted if layer 24 is entended to cover theentire inner surface of the tire, the air barrier layer 18 may beeliminated entirely from the vehicle tire construction.

Referring now in particular to the bicycle tire sealant embodiment ofthe present invention and with reference to FIG. 4, a bicycle tire 30conventionally includes a tread portion 32 and a carcass portion 34 withside walls 36. In bicycle tires, an inner tube 38 is generally disposedwithin the carcass portion 34, and provides the support and rigid shapefor the tire 30 when filled with compressed air. In accordance with thepresent invention, a sealant layer 40 is disposed on the inner surfaceof carcass portion 34 behind the tread portion 32 so as to be interposedbetween the carcass portion 34 and the inner tube 38.

Unlike the vehicle tire sealant layer, the bicycle tire sealant layer 40is generally not sprayed onto the inner surface of the tire 30. This isdue to the fact that the area for spraying is too small, and tire 30 isnot easily rotated, which is normally required for a uniformly thicklayer of sealant. In addition, the tire 30, without inner tube 38, lacksa rigid shape to work with inasmuch as the inner tube 38 provides thesupport for carcass portion 34. Therefore, the sealant 40 is preferablyformed into layers, as previously described, and then layed behind treadportion 32 between carcass 34 and inner tube 38 to be held in positionby inner tube 38. In addition, a suitable adhesive may be utilized bysecure layer 40 against carcass portion 34. The relative amounts of thevarious bicycle tire sealant constituents may be varied from those ofthe vehicle tire sealant composition due to different functionalrequirements of a bicycle tire as compared to a vehicle tire. A bicycletire is normally subjected only to an operational temperature range ofgenerally 30° to 125° F. Therefore, a bicycle tire sealant does notrequire high stength at very high temperature as does a vehicle tiresealant. Furthermore, the problem of creep which is present in a vehicletire sealant is not a factor in a bicycle tire sealant since it is notsubjected to very high temperatures, the centrifugal force loads imposedon a bicycle tire sealant are negligible as compared to the high loadsimposed on a vehicle tire sealant, and the bicycle tire sealant issandwiched between the tire's carcass portion and the inner tube andthereby trapped on both sides whereas the auto tire sealant is not.However, a bicycle tire sealant must be strong enough to keep from beingsqueezed out into the rim area by the pressure, probably up to 70 to 80pounds, within the inner tube. Therefore, the percentage of butyl rubberin the composition may be lower in the bicycle tire sealant than theamount in the vehicle tire sealant. In addition, the amount ofthermoplastic elastomeric block copolymer also may be lower and, infact, may be totally absent from the sealant composition.

The sealant compositions utilized in the following examples wereprepared by admixing the ingredients described below in the proportionsindicated by Table I. All proportions are given by weight.

                                      TABLE I                                     __________________________________________________________________________            Sealant Compositions (parts by weight)                                __________________________________________________________________________    Ingredient                                                                            A    B    C     D    E    F    G    H                                 __________________________________________________________________________    High Molecular                                                                Weight Butyl                                                                          9.5  9.5  10.03 14.25                                                                              9.0  14.5 10.4 4.8                               Rubber.sup.1                                                                  Low Molecular                                                                 Weight Butyl                                                                          14.5 14.5 15.04 9.5  13.0 9.5  6.9  19.2                              Rubber.sup.2                                                                  Tackifier.sup.3                                                                       61.75                                                                              61.75                                                                              65.16 62.0 63.75                                                                              61.75                                                                              60.0 61.75                             Carbon Black                                                                          9.5.sup.4                                                                          9.5.sup.4                                                                          4.76.sup.5                                                                          9.5.sup.4                                                                          9.5.sup.4                                                                          9.5.sup.4                                                                          17.2.sup.6                                                                         9.5.sup.4                         Block   4.75 4.75 5.01  4.75 4.75 4.75 5.0  4.75                              Copolymer.sup.7                                                               Para                                                                          Quinone 2.5  2.5  2.5   2.5  2.5  2.5  4.0  2.5                               Dioxime*                                                                      Benzoyl 7.9  7.0  7.9   10.0 7.9  7.0  10.0 7.9                               Peroxide*                                                                     __________________________________________________________________________     .sup.1 A copolymer was used consisting of 98.5% isobutylene and 1.5%          isoprene by weight having average molecular weight between 10,000 adn         300,000, available from Exxon Oil Company under Trademark "Butyl 365".        .sup.2 A copolymer was used consisting of 96% isobutylene and 4% isoprene     by weight having average molecular weight between 10,000 and 30,000,          available from Exxon Oil Company under Trademark "Butyl LM-43".               .sup.3 A polymer was used consisting of 98% isobutylene and 2%                isoparaffins, having average molecular weight between 500 and 5,000,          available from American Oil Company under Trademark, "Idopol H-300".          .sup.4 A furnace black was used having a surface area of 235 square           meters/gram, arithmetic mean particle diameter of 17 millimicrons, and a      pH of 9.0 available from Cities Service Oil Company under Trademark           "Raven-2000".                                                                 .sup.5 A furnace black was used having a surface area of 96 square            meters/gram, arithmetic mean particle diameter of 29 millimicrons, and a      pH of 8.0 available from Cities Service Oil Company under the Trademark       "Raven-1000"-                                                                 .sup.6 A carbon black composition was used consisting by weight of two        parts of high abrasion furnace black (HAF), one part semireinforcing          furnace black (SRF), and one part medium thermal black (MT).                  .sup.7 A block copolymer was used having a configuration A-(B-A).sub.1-5      representing a polystyrene block and B representing a hydrogenated            polyisoprene block, the isoprene making up about two thirds of the            compound by weight, and the average molecular weight being between 70,000     and 150,000. The compound is available from the Shell Oil Company under       Trademark "Kraton G-6500"-                                                    *In parts by weight per 100 parts of total butyl rubber.                 

EXAMPLE I

A vehicle tire sealant was prepared according to the formula ofcomposition "A" above. The butyl rubber and the block copolymer werefirst refluxed in toluene for 16 hours at about 250° F. After refluxing,the remaining components, except for the benzoyl peroxide, were added tothe mixture, along with additional toluene so that the toluene comprisedabout 50% of the mixture by weight. Just prior to applying thecomposition to a tire, 7.9 parts by weight of benzoyl peroxide per 100parts of butyl rubber components were dissolved in 60 parts of tolueneand added to the curable rubber composition.

New Uniroyal JR-78-15 steel belted radial tires were utilized forevaluating the subject sealant composition. The tires were first cleanedby mounting them on a rotator and then applying a one half gallon soapsolution containing 50 milliliters of Amway SA-8 soap powder. A steelrotary brush on a flexible cable then was used to scrub the tires withthe soap solution when the tires were rotating. Each tire was thenthoroughly rinsed out with tap water and dried at ambient (70° F)temperature prior to coating its inside surface with the sealantcomposition.

To apply the above composition "A" to the tire, the tire was firstpreheated to about 125° F for approximately one half hour. The tire wasthen removed from the oven and a quantity of the subject sealantcomposition, prepared as described above, was provided, including thebenzoyl peroxide activator. The sealant composition, dispersed intoluene, was then sprayed onto the inner surface of the cleaned andpreheated tire employing commercial air paint spray equipment. Apressure feed was employed and the sealant was sprayed using 50 psigcompressed air. The tire was rotated as the sealant was sprayed onto theinternal surface and directed to the region behind the tread as shown inFIG. 1. Approximately 290 grams, on a solvent free basis, of thecomposition "A" were applied. Some of the toluene evaporated during thespraying and the applied composition gelled in the tire in about fiveminutes. The tire was then left at ambient temperature for approximatelyone half hour to evaporate any excess toluene solvent and to cure thesealant composition layer.

The cycle of heating, spraying and setting was repeated two more timesin identical fashion, except that after the third spraying, the tire wasset aside and allowed to remain at ambient temperature for approximately30 days in order to age and reach its final cure properties. Theresultant coating had approximately 870 grams of the solid compositionand was approximately 0.100 inches thick. The amount of the layerapplied to a tire may, however, be larger or smaller than the above 870grams depending on the size of the tire and desired sealing performance.

In order to test the sealant composition's ability to seal a puncturewound in the tire, a tire was mounted on a wheel and inflated with airto about 28 psig. The wheel and tire were then mounted on an axle androtated at approximately 5 miles per hour against a free rotating wheelduring the puncturing test. Pressure was applied on the axle against thefree rotating wheel to obtain a load approximately 900-1000 pounds. Thetire was then punctured with two spikes of 0.265 inches thick indiameter, with one spike puncturing the center rib of the tread and theother spike puncturing the outside rib of the tread. These dynamic testswere performed at ambient temperature (about 70° F). After puncturing,the tire was run fifteen minutes with the nails in place after which thenails were removed. The pressure within the tire was then monitoredevery hour for approximately eight hours or until the pressure haddropped to 15 psig if there was in fact a leak. Also, after removal ofthe nails each puncture was squirted with a commercial soapy leakdetector called "Snoop" to visually observe if any leakage took place.It should also be noted that static puncturing tests were performed onthe tire at temperatures of -20° F and 270° F., and the nails utilizedin these static tests were 0.375 inches thick in diameter. In each testinstance, the tire containing the composition "A" of the presentinvention sealed each puncture without any significant leakage of air.

Another test was performed to determine the stability of the composition"A" and whether it would flow within the tire during high speed and hightemperature conditions. The tire containing the subject sealantcomposition was run on a smooth test wheel, 67.23 inches in diameter.(85mph on the test wheel was equivalent to at least 100 mph underhighway conditions, and the curved surface of the wheel caused moreflexing of the tire than a flat surface.) When the tire containing thecomposition "A" was run on the wheel for 3 hours at 90mph and at 264° F,it was determined after cutting into the tire that only a minor flow ofthe sealant had occurred, and the sealant was therefore quite stable.

EXAMPLE II

Tire sealant compositions according to the formula of compositions "B"and "C" above were prepared and applied to new tires in the same manneras described in Example I above. The type of tire used was also thesame. Puncture sealing tests using 0.265 inch nails were then run in thesame manner as in Example I. The results were the tires having the "B"or "C" compositions were sealed without any significant leakage of air.

EXAMPLE III

Tire sealant compounds according to the formula of compositions "E" and"F" above were prepared and applied to tires as in Example I. The tiresused were the same as in Example I. Stability tests were then performedin the manner of Example I. The tires having composition "F" were runfor two hours at 80mph and 224° F., 2 hours at 90mph and 246° F., and 2hours at 95mph and 292° F. Only a minor flow of sealant was observed.The tire having composition "F" was run for 3 hours at 90mph and 262° F,resulting in only a minute amount of sealant flow.

EXAMPLE IV

A tire sealant compound according to the formula of composition "G" wasprepared and applied to a tire as in Example I, except that only 200grams of the compound, on a solvent free basis, were applied at eachspraying, and the tire was alowed to set overnight rather than forthirty days after the final sealant application. The tire was thenmounted on a wheel and inflated with air to 30 psig. The wheel wasrotated and the tire was punctured with 0.20 and 0.25 inch diameterspikes at temperatures of -20° F, ambient, and 270° F. and the spike wasremoved. After puncturing at each temperature, each puncture wassquirted with "Snoop" to observe if any leakage took place. The tiresealed itself without any significant leakage of air.

EXAMPLE V

A tire sealant compound according to the formula of composition "D" wasprepared and applied to a tire as in Example IV, except that after thethird 200 gram sealant application the tire was set aside for an hour atambient temperature and then cured for 16 hours at 125° F. The puncturetests described in Example IV were then performed. In each instance, thesealant healed the puncture without significant loss of air.

EXAMPLE VI

A number of tackifiers other than "Indopol H-300" were investigatedduring the search for the optimium sealant composition. "Indopol"polybutylenes are available in a number of molecular weight ranges,including a low molecular weight variety, "Indopol H-50", and a highmolecular weight variety "Indopol H-1900". All of these were found tohave utility for environmental conditions that did not subject thesealant composition to high temperature.

Terpene polymer resins such as "Piccolyte S-10", a resin of B-pineneavialable from Hercules Incorporated were found quite satisfactory,having good high temperature cohesion and stability.

Low molecular weight styrene polymer resins such as "Piccolastic E-50",a polymer of A-methylstyrene available from Hercules Incorporated, werefound quite satisfactory in combination with other tackifiers up toabout 50 wt.% of the tackifier constituent.

In general, it was found that suitable high temperature tackifiers werethose with softening points of not greater than 50° C.

EXAMPLE VII

A sealant composition according to the formula of combination "H" wasprepared in the same manner as described in Example I above. The sealantwas applied to a flat surface and allowed to cure. Tensile tests wereperformed on specimens of the composition from which it was determinedthat the modulus of elasticity was substantially constant and that thecomposition was exceedingly soft. To perform as a tire sealant, thebutyl rubber content, of a 20/80 ratio, should be in the range of 30-40%by weight with a concommitant decrease in the weight % of the tackifier,all other constituents of composition "H" remaining the same.

EXAMPLE VIII

A sealant composition according to the formula of composition "B" wasprepared in the same manner as in Example I. Instead of being sprayed,however, the composition was poured onto a flat surface and a draw downbar was drawn over the surface to produce a flat sealant layer. Aftercuring, the sealant was cut into strips which were applied to bicycletires as depicted in FIG. 4. The tires were standard medium weightbicycle tires, and were inflated to 45 psig. Nails having 0.115 inchdiameters were inserted into the tires and then removed. No significantloss of air was detected.

With the exception of sealant composition "H", the sealant compositionsused in the foregoing examples were found to have moduli of elasticityin the range of 5 to 9 lbs/in.². Above 9 lbs/in.², the sealant would betoo stiff to self heal after a puncturing object was removed. Below 5lbs/in.², the sealant would creep at combinations of centrifugal forceand temperature to be expected in a vehicle tire. The preferred range ofmost effective tire sealants is between 6 and 8 lbs/in.². By increasingthe weight % of butyl rubber in composition "H", as described in ExampleVII, the composition "H" modulus of elasticity, still remainingsubstantially constant, would be brought within the preferred range. Forother applications, the degree of butyl rubber cross-linking may bevaried to produce higher or lower modulii of elasticity as required bythe particular environment.

As can be seen from the above, the present sealant composition not onlyelinimates the problems of high speed and high temperature sealant flowas well as sufficient tensile strength, but the subject invention, dueto its unique and novel ratio of high to low molecular weight curablebutyl rubbers, results in considerably improved puncture sealingcapabilities, especially when the puncturing object remains in the tire.In addition, the sealant composition of the instant invention may alsobe utilized for numerous other purposes including uses as a tire patch,an auto sealant, a roofing sealant, a caulking compound, a generalhousehold sealant and others.

It will be understood that the invention may be embodied in otherspecific forms without departing from the spirit or centralcharacteristics thereof. The present examples and embodiments,therefore, are to be considered in all respects as illustrative and notrestrictive, and the invention is not to be limited to the details givenherein but may be modified within the scope of the appended claims.

What is claimed is:
 1. A sealant composition comprising a reinforcedpartially cross-linked matrix comprising a high average molecular weightbutyl rubber having a molecular weight in the range of approximately100,000 to 400,000 and a low average molecular weight butyl rubberhaving a molecular weight in the range of approximately 10,000 to40,000, in a ratio of high to low molecular weight butyl rubber ofbetween about 35/65 and 45/55, in admixture with a tackifier present inan amount between about 55 and 70 weight % of the composition.
 2. Thesealant composition of claim 1, wherein the high molecular weight butylrubber and the low molecular weight butyl rubber are comprised of amajor proportion of isobutylene.
 3. The sealant composition of claim 1,wherein the high molecular weight butyl rubber and the low molecularweight butyl rubber consist of between about 96% to 99% by weightisobutylene and between about 4% to 1% by weight isoprene.
 4. Thesealant composition of claim 1, including a partially hydrogenated blockcopolymer in admixture with the matrix, said block copolymer having thegeneral configuration A--(B--A)₁₋₅ wherein each A is a monovinyl arenepolymer block and each B is a substantially fully hydrogenatedconjugated diene polymer block.
 5. The sealant composition of claim 4,wherein the partially hydrogenated block copolymer is present in anamount up to about 10% of the total composition by weight.
 6. Thesealant composition of claim 1, wherein the tackifier is selected fromthe group consisting of synthetic polyterpenes, thermoplastic olefins,pentaerythritol esters of hydrogenated rosins, thermoplastichydrocarbons, triethylene glycol esters of hydrogenated rosins, vinyltoluene copolymers, alkyl aromatics, coumarone-indenes and methyl estersof hydrogenated rosins.
 7. The sealant composition of claim 1, whereinthe tackifier is selected from the group consisting of polymers ofbutylene, terpene polymer resins and low molecular weight styrenepolymer resins.